The spinal column consists of thirty-three bones called vertebra, the first twenty-four vertebrae of which make up the cervical, thoracic, and lumbar regions of the spine and are separated from each other by “pads” of tough cartilage called “intervertebral discs,” which act as shock absorbers that provide flexibility, stability, and pain-free movement of the spine.
FIGS. 1 and 2 illustrate a portion of a healthy and normal spine, and specifically, two vertebra 10 and two intervertebral discs 12 (only one shown). The posterior of the vertebra 10 includes right and left transverse processes 14R, 14L, right and left superior articular processes 16R, 16L, and a spinous process 18. Muscles and ligaments that move and stabilize the vertebra 10 are connected to these structures. The vertebra 10 further includes a centrally located lamina 20 with right and left lamina 20R, 20L, that lie inbetween the spinous process 18 and the superior articular processes 16R, 16L. Right and left pedicles 22R, 22L are positioned anterior to the right and left transverse processes 14R, 14L, respectively. A vertebral arch 24 extends between the pedicles 22 and through the lamina 20. The anterior of the vertebra 10 includes a vertebral body 26, which joins the vertebral arch 24 at the pedicles 22. The vertebral body 26 includes an interior volume of reticulated, cancellous bone (not shown) enclosed by a compact cortical bone 30 around the exterior. The vertebral arch 24 and vertebral body 26 make up the spinal canal (i.e., the vertebral foramen 32), which is the opening through which the spinal cord 34 and epidural veins (not shown) pass. Nerve roots 36 laterally pass from the spinal cord 34 out through the neural foramen 38 at the side of the spinal canal formed between the pedicles 22. Structurally, the intervertebral disc 12 consists of two parts: an inner gel-like nucleus (nucleus pulposus) 40 located centrally within the disc 12, and tough fibrous outer annulus (annulus fibrosis) 42 surrounding the nucleus 40.
A person may develop any one of a variety of debilitating spinal conditions and diseases. For example, as illustrated in FIG. 3, when the outer wall of the disc 12′ (i.e., the annulus fibrosis 42) becomes weakened through age or injury, it may tear allowing the soft inner part of the disc 12 (i.e., the nucleus pulposus 40) to bulge out, forming a herniation 46. The herniated disc 12′ often pinches or compresses the adjacent dorsal root 36 against a portion of the vertebra 10, resulting in weakness, tingling, numbness, or pain in the back, legs or arm areas.
Often, inflammation from disc herniation can be treated successfully by nonsurgical means, such as bedrest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosterioids, and anesthetics. In some cases, however, the disc tissue is irreparably damaged, in which case, surgery is the best option.
Discectomy, which involves removing all, or a portion, of the affected disc, is the most common surgical treatment for ruptured or herniated discs of the lumbar spine. In most cases, a laminotomy or laminectomy is performed to visualize and access the affected disc. Once the vertebrae, disc, and other surrounding structures can be visualized, the surgeon will remove the section of the disc that is protruding from the disc wall and any other offending disc fragments that may have been expelled from the disc. In some cases, the entire disc may be removed, with or without a bony fusion or arthroplasty (disc nucleus replacement or total disc replacement).
Open discectomy is usually performed under general anesthesia and typically requires at least a one-day hospital stay. During this procedure, a two to three-inch incision in the skin over the affected area of the spine is made. Muscle tissue may be separated from the bone above and below the affected disc, while retractors hold the wound open so that the surgeon has a clear view of the vertebrae and disc and related structures. The disc or a portion thereof, can then be removed using standard medical equipment, such as rongeurs and curettes.
Because open discectomy requires larger incisions, muscle stripping or splitting, more anesthesia, and more operating, hospitalization, and a longer patient recovery time, the trend in spine surgery is moving towards minimally invasive surgical techniques, such as microdiscectomy and percutaneous discectomy.
Microdiscectomy uses a microscope or magnifying instrument to view the disc. The magnified view may make it possible for the surgeon to remove herniated disc material through a smaller incision (about twice as small as that required by open discectomy) with smaller instruments, potentially reducing damage to tissue that is intended to be preserved.
Percutaneous discectomy is often an outpatient procedure that may be carried out by utilizing hollow needles or cannulae through which special instruments can be deployed into the vertebra and disc in order to cut, remove, irrigate, and aspirate tissue. X-ray pictures and a video screen and computer-aided workstation may be used to guide by the surgeon into the treatment region. Improved imaging and video or computer guidance systems have the potential to reduce the amount of tissue removal required to access and treat the injured tissue or structures. Sometimes an endoscope is inserted to view the intradiscal and perivertebral area.
Besides disc hernias, other debilitating spinal conditions or diseases may occur. For example, spinal stenosis, which results from hypertrophic bone and soft tissue growth on a vertebra, reduces the space within the spinal canal. When the nerve roots are pinched, a painful, burning, tingling, and/or numbing sensation is felt down the lower back, down legs, and sometimes in the feet. As illustrated in FIG. 2, the spinal canal 32 has a rounded triangular shape that holds the spinal cord 34 without pinching. The nerve roots 36 leave the spinal canal 32 through the nerve root canals 38, which should be free of obstruction. As shown in FIG. 4, hypertrophic bone growth 48 (e.g., bone spurs, osteophytes, spondylophytes) within the spinal canal 32, and specifically from the diseased lamina 20 and proximate facet joints may cause compression of the nerve roots, which may contribute or lead to the pain of spinal stenosis. Spinal stenosis may be treated by performing a laminectomy or laminectomy in order to decompress the nerve root 36 impinged by the bone growth 48. Along with the laminectomy, a foraminotomy, (i.e., enlarging of the channel from which the nerve roots 36 exit is performed). Depending on the extent of the bone growth, the entire lamina and spinal process may be removed.
Another debilitating bone condition is a vertebral body compression fracture (VCF), which may be caused by spinal injuries, bone diseases such as osteoporosis, vertebral hemangiomas, multiple myeloma, necorotic lesions (Kummel's Disease, Avascular Necrosis), and metastatic disease, or other conditions that can cause painful collapse of vertebral bodies. VCFs are common in patients who suffer from these medical conditions, often resulting in pain, compromises to activities of daily living, and even prolonged disability.
On some occasions, VCFs may be repaired by cutting, shaping, and removing damaged bone tissue inside a vertebra to create a void, and then injecting a bone cement percutaneously or packing bone graft into the void. This is typically accomplished percutaneously through a cannula to minimize tissue trauma. The hardening (polymerization) of a bone cement media or bone grafting or other suitable biomaterial serves to buttress the bony vault of the vertebral body, providing both increased structural integrity and decreased pain that may be associated with micromotion and progressive collapse of the vertebrae.
Thus, it can be appreciated that in many spinal treatment procedures, bone and/or disc tissue must be removed in order to decompress neural tissue or rebuild the bony vertebra or intervertebral disc. In the case of target bone tissue that is adjacent spinal tissue, a physician is required to exercise extreme care when cutting away the target bone tissue (e.g., during a laminectomy and foraminotomy), such that injury to spinal tissue can be prevented. A physician may have difficulty controlling existing bone removal devices, however, and may unintentionally remove healthy bone tissue or injure spinal tissue during use. This problem is exacerbated with percutaneous treatments, which, although less invasive than other procedures, limit the range of motion of the cutting instrument, thereby further limiting the control that the physician may have during the bone cutting procedure.
Burr-type tissue removal probes may also be used to remove soft tissue, such as the gel-like nuclear tissue within the intervertebral disc or the cancellous bone tissue within the vertebral body. For example, FIG. 5 illustrates one prior art burr-type tissue removal probe 50 that can be introduced through a delivery cannula (not shown) into contact with the target tissue region to be removed. The tissue removal probe 50 comprises a rigid shaft 52 and a rotatable burr 54 associated with the distal end of the rigid shaft 52. Rotation of a drive shaft 56 extending through the rigid shaft 52, in turn, causes rotation of the burr 54 (either manually or via a motor), thereby removing tissue that comes in contact with the burr 54. Notably, the tissue removal probe 50 is laterally constrained within the cannula (or if a cannula is not shown, constrained by the many layers of tissue that the device 50 must traverse to reach the target tissue), and thus, can only be effectively moved along its longitudinal axis, thereby limiting the amount of tissue that can be removed to the tissue that is on-axis. As such, the tissue removal probe 50 may have to be introduced through several access points within the anatomical body (e.g., the disc or vertebral body) that contains the target tissue in order to remove the desired amount of the tissue.
As illustrated in FIG. 6, the distal end 58 of the rigid shaft 52 may be curved in an alternative prior art removal device 60, so that the burr 54 is off-axis from the shaft 52. As such, off-axis target regions can be reached by rotating and axially displacing the rigid shaft 52 about its axis. Because the length of the curved distal end is fixed, however, only the tissue regions that are off-axis by a distance equal to the off-axis distance of the burr 54 will be removed, as illustrated in FIG. 7. In effect, the removal device 60 can only remove a cylindrical outline 62 of the tissue, leaving a cylindrical tissue body 64 behind. Thus, the tissue removal probe 60 must still be introduced into the tissue via several access holes in order to remove any remaining tissue.
In addition, because the distal end of the rigid shaft 52 is curved and has a length of the distal tip that is now at an angle to the main shaft, the delivery cannula must be made larger to accommodate the entire profile of the distal end. Thus, the incision through which the cannula is introduced must likewise be made larger. Lastly, if the anatomical body in which the removal device 60 is introduced is relatively thin (e.g., an intervertebral disc is a few millimeters thick), the top or bottom of the anatomical body may hinder movement of the burr 54 as the shaft 52 is rotated around its axis. In such cases, the removal device 60 may have to be introduced along the bottom of the anatomical body to allow tissue to be removed at the top of the anatomical body (i.e., by sweeping the burr 54 along an upper arc until the burr 54 hits the top, or if clearance at the top is available, by sweeping the burr 54 along the upper arc, below the top, until the burr 54 hits the bottom), and then reintroduced along the top of the anatomical body to allow tissue to be removed at the bottom of the anatomical body (i.e., by sweeping the burr 54 along a lower arc until the burr 54 hits the bottom, or if clearance at the bottom is available, by sweeping the burr 54 along the lower arc, above the bottom, until the burr 54 hits the top). As can be appreciated, this excessive movement of the removal device 60 increases the time of the spinal procedure as well as surgical risk due to manipulation of the device.
Another problem with current burr-type removal devices is that soft material, such as the nuclear material in an intervertebral disc or cancellous bone within the vertebral body, tends to stick to the burrs, thereby limiting the abrasive effect that the burrs are intended to have in order to efficiently remove tissue. As a result, burr-type removal device may have to be continuously removed from the patient's body in order to clean the soft tissue from the burr.
Furthermore, during the tissue removal or cutting process, a media, such as saline, is generally delivered via a tube to a target site for clearing debris. The delivered media together with the debris are then removed from the target site via a separate tube (i.e., the media and the debris are aspirated into a vacuum port of the tube). When the spine is treated percutaneously, however, the delivery cannula must be made large enough to accommodate the tissue removal probe and tubes. As a result, the incision through which the cannula is to be introduced must be made relatively large, thereby unnecessarily causing more tissue trauma.
There, thus, remains a need to provide for improved tissue removal probes and methods for use during spinal treatment and other surgeries.